Piezoelectric crystal holder



R. SMOLUCHOWSKI 2,460,153 PIEZOELECTRIC I C RYSTAL HOLDER Filed July 30, 1946 Jan. 25; 1949,

Fig.2.

Inventor: Roman SmOIUChOWSkI b W His Attorney.

Patented Jan. 1949 PIEZOELITCTBIC CRYSTAL HOLDER no? smolnclimki, Pit

tslmrgh, 1's... assignor General Electric corporation of "New .Ysrk

application July "r1948, Serial No. 887,201 1. Claims. (Cl. 171-427) 1 My invention relates to piezoelectric crystal holders and more particularly to a new and improved holder for crystals used in exploring materials by supersonic vibrations.

Nondestructive methods of testing materials,

such as metals, to determine flaws, holes; cracks,

and the like within the material have been developed. One of these methods involves the study of the transmission, attenuation and reflection characteristics of a specimen subjected to a wave train of sonic or supersonic vibrations either pulsed-or continuous.

Piezoelectric crystals are usually employed as the transmitter as well as the receiver of these waves. If a crystal is held firmly against a chosen surface of the specimen and set into' vibration b the usual electrical means, waves will travel into that portion of the material approximately enclosed by a cone whose axis is herpes-- dicular to the crystal and its apex is at the crystal.

An oil film between the crystal and material tested is usually employed to improve the coupling between the two. The thickness of the oil film is not critical and in fact the crystal may be operated at an angle with respect to the adjacent surface of the material with good results. Thus the waves need not be propagated into the material in a direction perpendicular to the surface of the material at their origin but in traveling in a direction perpendicular to the crystal may travel obliquely into the material.

- It is desirable to realize this advantage since in irregularly shaped specimens it may not be possible to explore all portions of the specimen from the flat surfaces it may possess unless the waves are made to enter obliquely as well as perpendicularly with respect to these surfaces.

out in the claims appended hereto. For a better understanding of the invention reference is made in the following description to the accompanying drawing in which Fig. 1 is a partially cutaway side view of one embodiment of my invention; Fig. 2 is a cross-sectional side view at right angles to Fig. 1; and Fig. 3 is a bottom view of the device.

Referring to the drawing and in particular to Fig. 1, a hollow cylindrical casing I, preferably of conducting metal, is provided with a circular opening 2 in one end-thereof of a diameter less than the inside diameter of the cylinder. A member 3, preferably constructed of a rigid insulating material and having a cylindrical head 4 and a stem 5, is placed within the casing I in such manner that the cylindrical head 4- is loosely fitted into opening 2 of casing I with stem I extending interiorly. The exposed surface of head 4 is provided with ridges to which one sur- ,face of a crystal 6 may be attached as by a It is an object of my invention to provide a new and improved piezoelectric crystal holder whereby the crystal is held at an adjustably ilxed angle with respect to the surface of the material being explored.

It is a further object of my invention to provide -a piezoelectric crystal holder which holds the crystal in contact with the material to be explored at a proper and constant surface pressure.

It is another object of my invention to provide a new and improved piezoelectric crystal holder of such structure that the crystal and its asso ciated electrical circuit .-is effectively shieldedfrom undesirable extraneous electrical and neon stical influences.

The features of the invention which are besuitable cement. Crystal 8 is designed to vibrate in a thickness mode and it is desirable to minimize the contact area between the crystal 8 and head 4 by using a ridged surface as shown which prevents excessive damping of the crystal caused by energy loss into head 4.

Head 4 is provided with an annular flange l flush with its interior surface. Flange I is of greater diameter than opening 2 in casing I, thereby acting as a stop limiting the extent to which head 4 may protrude from casing I.

To provide a proper pressure of crystal I against a material to be explored such as 8, a compression spring 9 urges head 4 outwardly through opening 2. An annular ring I II within casing I and affixed thereto provides a seating surface for spring 9.

The angle ofincidence between the crystal i and test material 8 may be adjusted by a tilting device constructed in the following manner. The end of stem 5 is provided with a rectangularly shaped sleeve II rigidly afiixed thereto. Diametrically opposed sectors I2 are ailixed to the interior of easing I to provide a guide or slot in which sleeve may be moved. The position of sleeve I'I within the slot may be adjusted by proper manipulation of adjusting screws I! through casing I and contacting opposing sides of sleeve II thereby adjusting the angle between stem! and the axis of casing I.

lieved to be novel and patentable will be pointed Electrode surfaces for crystal t are preferably provided by depositing metallized coatings on the opposite surfaces of the crystal. The inner electrode surface in contact with the ridged surface of head 4 is connected to the inner terminal' of connector plug 14 affixed to casing l by a lead 15, shown in Fig. 2, which passes through an axially disposed hole in head 4 and stem 5. The exposed surface electrode of crystal 6 is connected to the outer portion of connector plug H by contact with the conducting material to be explored which in turn is in contact with the casing l.

When exploring magnetic position of the crystal assembly may be maintained by use of magnets 16 afilxed to casing I in a position to exert a force of attraction upon the material. If these magnets are composed of material having a high coercive force such as a permanent magnet alloy, of aluminum nickel and cobalt, the force of attraction is sufllcient to hold the assembly in place with the crystal pressed against the test piece 8 even when inverted and placed on the under side of the magnetic material to be explored. Similarly positioned weights or other equivalent means may replace magnets I6 if desired when nonmagnetic materials are being explored.

The device as described assures proper and automatically reproducible pressure, determined by compression spring 9, between the crystal and the material-to be explored. It also enables the crystal to assume a desired angle with respect to the surface of the material being explored, which angle is adjustable and automatically reproducible at other chosen positions of the assembly for any setting of the adjusting screws I3. Any angle within which the oil film between the crystal and test material remains unbroken may be used. I have employed an angle of 10 with satisfactory results when using an oil film of heavy machine oil and a crystal /2 inch square.

When in operative position, the crystal is totally encompassed by conducting material so that pickup of extraneous electrical disturbances will not occur in or by the crystal holder assembly.

' As will occur to those skilled in the art, various different arrangements and combinations of the principles described above may be employed without departing from the true spirit and scope of the invention and I therefore do not wish to limit my invention to the particular arrangement described.

What I claim as new and desire to secure by Letters Patent of the United States is:

I 1. A piezoelectric crystal holder comprising a member possessing a surface adapted for mounting a crystal thereon and adapted to face a test piece, a base member, resilient means supported by said base member urging said member towards the surface of a test piece upon which said base member is adapted to be placed, means for adjustably fixing the angle between said crystal. mounting surface and an axis of said base member, and a stop to limitthe movement of said member in the direction urged by said resilient 7 means.

materials'the desired an eiectro-magnetic shield surrounding said crystal mounting member for shielding said member from extraneous electrostatic and electromagnetic effects.

3. A piezoelectric crystal holder comprising a casing with an opening therein, a member movably positioned within said casing and possessing a crystal mounting surface outwardly exposed in said opening, resilient means urging said surface outwardly through the opening in said casing, means for adjustably fixing the angle of inclination of said crystal mounting surface with respect to said casing and means within said casing limiting the outward travel of said surface through said opening.

4. A piezoelectric crystal holder comprising a casing with an opening therein, said casing being of conducting material thereby shielding its interior from extraneous electrical effects, a member movably positioned within said casing and possessing a crystal mounting surface outwardly exposed in said opening, resilient means urging said surface outwardly through the opening in said casing, means for adjustably fixing the angle of inclination of said crystal mounting surface with respect to said casing and means within said casing limiting the outward travel of said surface through said opening. 5. A piezoelectric crystal holder comprising a hollow casing of conducting material having an opening in a wall thereof, an elongated member of insulating material movably supported in said casing with one end exposed in said opening, a piezoelectric crystal mounted on said exposed end, means for holding the casing against the surface of a test piece with the crystal facing such surface, resilient means within the casing for urging the elongated member towards the opening so as to press the crystal thereon against such surface and means for adjusting the longitudinal axis of said member within the casing to vary the angle of contact of said crystal on such surface.

6. A piezoelectric crystal holder comprising a hollow casing of conducting material having an opening in a wall thereof, an elongated member of insulating material movably supported in said casing with one end exposed in said opening, a piezoelectric crystal mounted on said exposed end,

means for holding the casing against the surface of a test piece with the crystal facing such surface, resilient means within the casing for urging the elongated member towards the opening so as to press the crystal thereon against such surface, means for adjusting the longitudinal axis of said member within the casing to vary the angle of contact of said crystal on such surface, an electrical connection insulated from said casing to one surface of said crystal, and' an electrical connection to said casing whereby the opposite surface of said crystal may be connected in an electric circuit through a test piece of conducting material when in contact with such test piece.

7. A piezoelectric crystal holder comprising a hollow casing of conducting material having an opening in the base thereof, an elongated member of insulating material movably supported 'in said casing with one end exposedin said opening, a piezoelectric crystal mounted on said exposed end and adapted for contact with the surface of a test piece upon which the base of said casing is adapted to be placed, resilient means within the casing for urging the elongated member towards the opening so-as to press the crystal thereon against such surface, and means for adlusting the longitudinal axis of said member within the casing to vary the angle of contact of said crystal on such surface. I 8. In a holder for maintaining a piezoelectric crystal in position against a surface, the combination of a base adapted to be held in a fixed position against such surface, a member adapted to have such crystal mounted thereon adjacent to and facing such surface, and a tilting device adjustably connecting said member to said base so that the crystal is held at an adjustabl'y fixed end thereof exposed in said opening, said end being adapted to have such crystal mounted thereon for contact with such surface, and a tilting device for radially displacing the other end of said member to tilt its axis.

0 Number 10. In a holder for maintaining a piezoelectric crystal in position against a surface at an adjustabiy fixed angle, the combination of a hollow casing having a base with an opening therein, said base being adapted to be held flush with such surface, an elongated member movably supported in said casing and having one end thereof exposed in said opening, said end being adapted to have such crystal mounted thereon for contact with such surface, and adjusting screws positioned to radially displace the other end of said member to tilt its axis.

ROMAN SMOLUCHOWSKI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Conklin May 9, 1933 Scofleld May 14, 1935 Erwin Nov. 18, 1947 

